Finishing of viscose-rayon



Search Room a-iae sa hi hl ht/ t messes as herswsz Patented June 27, 1933 "UNITED STATES PATENT OTFFlCE GEORGE A. RICHTER AND CHESTER H. GOLDSMITH, OF BERLIN, NEW HAMPSHIRE, AS- SIGNORS TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A QORPORATION OF MAINE FINISHING OF VISCOSE-RAYON No litrawilig.

This invention relates to the finishing of rayon, being more particularly concerned with the finishing of crude rayon produced by the so-called viscose-rayon process.

In the manufacture of viscose-rayon, the practice isto spin the viscose syrup through spinnerets into an acid salt'bath which serves to set the syrup as filaments, which issue continuously from the bath as yarn. The crude rayon yarn thus produced is usually accumulated in spool, cake, or skein form, and then is subjected to various chemical treatments designed to purify it and to improve luster,

whiteness, softness, and other silk-like qualities. The crude yarn may vary in color from amber to light tan, depending upon the process of manufactureand the purity of the cellulose pulp used as a raw material in'the pro ductlon of the viscose syrup. It is contaminated by the sulphur precipitated when the viscose is set in the acid bath, thisi'mpurity impairing its luster. The usual'finishingof viscose-rayon comprises desulphurizing and bleaching steps, desulphurization hav ng heretofore been effected before bleaching .in order to ensure the removal of coloring substance generated during desulphurization, as

well as those present in the original crude onstrated that, whereas the yarn undergoes marked loss in strength and is quite sensitive to oxidation after treatment with solutions of desulphurizing agents such as sodium sulphide, it undergoes little, if any, loss n strength or oxidation if whitened with oxidizing bleaching agents prior to desulphurization. In order to avoid reaction between the residual bleaching agent carried by the yarn after bleaching and desulphurlzmg agents such as sodium sulphide employed in the subsequent step of desulphurization, the bleached yarn is preferably treated with'a solution of tion.

Application filed November 14, 1929. Serial No. 407,271.

a reducing agent capable of converting such residual bleach into While it is possible to employ solutions of various water-soluble reducing agents for this purpose, we prefer to use water-soluble aldehydes, such as formaldehyde, sodium sulphite, or other water-soluble agents which do not react with and precipitate sulphur from the sulphide class of desulphurizing agents, such as sodium sulphide, ammonium sulphide, or the like. The use of such reducing agents makes possible dispensing with a step of washing after treatment with reducing agents, and at the same time permits using sulphide desulphurizing agents, which are advantageous in that they effect a more rapid and complete desulphurization than other classes of desulphurizing agents. After desulphurization has been eflected, the yarn may be washed free .of desulphurizing agent and reaction products, whereupon it is preferably supeibleached with agents such as permanganate, sodium peroxide, or peroxide solutions which do not materially adversely affect the strength or other qualities of the yarn in concentrations and under such conditions as are necessary for merely a superbleaching opera- Such superbleaching agents may be more expensivethan the bleaching agent used for bleaching the crude yarn, but it is necessary toemploy only comparatively dilute solutions of such agents, as the yarn is already white, and when treated with these dilute solutions acquires brilliant whiteness. WVhen permanganate solutions are employed for superbleaching, it is preferable that they be neutral or slightly acid, as alkaline permanganate solutions have been found to lower the strength of the yarn. After permanganate superbleaching, the yarn may be treated .with a suitable reducing agent, such as a inactive products.

sulphurous acid solution, to reduce residual permanganate to colorless manganous salts,

whereupon the yarn may be washed in a soap solution, which enhances softness and serves to deposit a soap film which acts as a lubricant during subsequent weaving or knitting operations.

The process of the present invention may be applied to rayon after it has been accumulated, for instance on spools or in centrifuge baskets, or has been reeled into skeins. It may, however, be practiced with especial advantage upon rayon coming from the setting 6 bath before it'is accumulated in accordance with the disclosure of application Serial No. 356,426, filed April 19, 1929, by George A. Richter. In actual practice, where multiple spinning machines are employed, the yarns 10 coming from one or a series of acid setting baths may be passed through a series of treating baths such as hereinafter described, before being accumulated. Assuming that the viscose s rup has been spun into the usual acid setting bath, for instance asolution of sulphuric acid and sodium sulphate, the crude yarn issuing from the setting bath is preferably first'washed free of acid solution carried 1 thereby. This may be accomplished by passing the yarn through a bath of water, for

instance at 80 C., which not only serves to wash water-soluble constituents, including acid, from the yarn, but to convert any residual xanthate into regenerated cellulose. The yarn may then be assed through a bath of suitable oxidizing b each solution, for instance chlorme water or calcium or sodium lonitembleach solution, containing 1% available chlorine and at 20 to 25 C. When hypochlorite bleach is employed, it is prefera- 85 about 04% caustic soda for this purpose.

The bleached yarn is then passed through a bath of suitable reducing solution, for instance a 1% solution of formaldehyde at 20 to 25 C; Preferably, the formaldehyde 40 solution is also alkaline and contains an alkali such as caustic soda to the extent of about 1%, as the alkali accelerates the reaction between the formaldehyde and residual bleach carried by the yarn into the reducing solution and further serves to prevent decomposition of the formaldehyde. The yarn is then passed through a bath of suitable desulphurizing solution, preferably containing a sulphide desulphurizing agent such as sodium sulphide, ammonium sulphide, or potassium sulphide. If desired, other desulphurizing agents, such as caustic soda, sodium carbonate, or sodium sulphite, may be used along with the sulphide. The desulphurizing solution may be one containing about 5% sodium sulphide, in which case it is preferably maintained hot, for instance at 80 (3., in order to accelerate desulphuriza tion. The desulphuriz'ed yarn is then passed through a bath of water preferably maintained hot, say,.at 80 0., under which temperature not only are water-soluble chemicals readily removed, but further desulphurization is effected. The washed yarn may be 85 accumulated as on a spool or in a cake, dried,

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twisted, and converted into skeins for fabric manufacture.

It is preferable, however, to subject the washed yarn to further chemical treatment prior to accumulation.- The washed yarn may be supcrbleached to high whiteness .without material injury thereto, by passing it through a bath of suitable bleach solution, for instance an acid solution of potassium permanganate or a solution of the peroxides of hydrogen, sodium, or potassium. Such superbleaching solutions. may be comparatively dilute, as the yarn contains but little coloring matter at this stage. F or instance, a suitable superbleaching solution may contain but 3% potassium permanganate and 1% hydrochloric acid-and be at 20 to 25 C., as under these conditions a brilliant white product is obtained practically without reducing the strength of the yarn. The superbleached yarn may then be passed through a bath of water at 25 C. to remove watersoluble chemicals, whereupon it may be passed through a bath of a suitable reducing solution, for instance a .1%' sulphurous acid solution at 20 to 25 C., which serves to reduce residual-permanganate to colorless manganous salts. The yarn may then be passed through a bath of water, which serves to remove water-soluble chemicals. Preferably, the water contains a small amount of suitable soap, for instance ,7 monopole or coconut oil soap, and is maintained at 40 to 45 (1., under which conditions the yarn is enhanced in softness and is lubricated for subsequent fabricating operations.

The method hereinbefore described may be carried out without encountering serious breakage of yarn or other difliculties, the yarn being spun at the rate of, say, 50 meters per minute, and a portion of the yarn of the desired length, for instance 12 feet, being immersed in each of the baths to ensure thorough treatment. It.may be applied to the usual 24-filament, 150 dernier yarn or yarns of the same weight composed of more filaments, in which latter case it is especially desirable -to treat the yarn before accumulation, as more filaments are thoroughly and uniformly treated with the desired chemical solutions and Water before accumulation, so that the product is characterized by unusually good luster, softness, and other silk-like prop-' ertles.

When rayon yarn is finishedin accumulated form, it may be advantageous to modify the strength of solutions used in the various treatments, as'in such case the solutions'must penetrate through and react upon a compact mass 'of yarn; In such case, too, certain of the benefits hereinbefore' enumerated are realized. By bleaching the accumulated crude yarn before 'desulphurization, it is apparently possible to affect more thorough de'sulphurization as the removal of coloringimpurities from the filaments makes possible a more rapid and uniform penetration of desulphurizing solution throughout the compact mass of yarn.

What we claim is:

1. A process which comprises treating crude viscose-rayon with an oxidizing bleach solution, treating with a solution of an agent capable of reducing residual bleach carried by the rayon to an inactive condition, and treating with a desulphurizing agent.

2. A process which comprises treating crude viscose-rayon successively with solutions of (a) an oxidizing bleach, (b) a. reducing agent incapable of reacting with a sulphide desulphurizing solution, (0) and a "sulphide desulphurizing solution.

3. A process which comprises treating crude viscose-rayon with an oxidizing bleach solution, treating with a formaldehyde solution to reduce'residual bleach carried by the rayon to an inactive condition, and treating with a desulphurizing agent.

4. A process of finishing crude viscoserayon, which comprises initially bleaching the rayon, desulphurizing, and superbleaching substantially without affecting the strength of the rayon.

5. A process of finishing crude viscoserayon, which comprises initially bleaching the rayon, desulphurizing, and superbleaching in an acid permanganate solution.

6. A process of finishing crude Viscoserayon, which comprises initially bleaching the rayon, desulphurizing, and superbleaching in a non-alkaline permanganate solution.

7. A process which comprises treating crude viscose-rayon with chlorine water, treating with a solution of an agent capable of reducing residual oxidizingagent carried by the rayon to an inactive condition, and

treating with a reducing desulphurizing agent.

8. A process which comprises treating crude viscose-rayon with hypochlorite bleach solution, treating with a solution of an agent ried by the rayon to an inactive condition,

and treating with a sulphide desulphurizing vsolution.

11. A process which comprises treating I crude viscose-rayon with an oxidizing bleach solution, treating with a solution of formaldehyde to reduce residual bleach carried by the rayon to an inactive condition, and treating with a sulphide desulphurizing solution. 12. A process which comprises treating crude viscose-rayon with an oxidizing bleach solution, treating witha solution of sodium s'ulphite to reduce residual b ach carried by the rayon to an inactive condition, and treating with a sulphide desulphurizing solution. In testimony whereof we have affixed our signatures.

' GEORGE A. RICHTER.

CHESTER H. GOLDSMITH. 

